Biogas production from excrement

ABSTRACT

A method for producing biogas includes: anaerobically digesting excrement with an additive, the additive including a pre-pupal stage of an insect from the scientific classification superfamily of Stratiomyoidea; and collecting the biogas. A method for producing an additive for anaerobic digestion of excrement includes: hatching eggs of an insect from the scientific classification superfamily of Stratiomyoidea in excrement; growing insect larvae by feeding with additional excrement; harvesting pre-pupal insect larvae; and grinding the pre-pupal larvae. An apparatus for producing an additive for anaerobic digestion of excrement includes: a tray having pivot along one lateral side and an upwardly sloping wall terminating with a lip along a lateral side opposite the pivot; a flume adjacent the lip; and a conveyor adjacent the pivot.

RELATED APPLICATIONS

This application claims the benefit of co-pending U.S. ProvisionalPatent Application Nos. 62/545,064 filed Aug. 14, 2017; 62/559,777 filedSep. 18, 2017; and 62/567,390 filed Oct. 3, 2017, each is incorporatedherein by reference; and co-pending U.S. Utility patent application Ser.No. 16/101,880 filed Aug. 13, 2018, now U.S. Utility Pat. No.10,947,565, incorporated herein by reference.

FIELD OF THE INVENTION

The inventions disclosed herein are directed to the production of biogasfrom excrement, particularly livestock generated excrement, using ananaerobic digestion process.

BACKGROUND OF THE INVENTION

Excrement can be converted to biogas. Biogas is a gaseous fuel producedby fermentation of organic matter and generally contains methane andcarbon dioxide, among other by-products of the fermentation process. Themore biogas that can be economically generated from excrement, the moreeconomical the excrement disposal process.

Large amounts of excrement are generated in the production of farmanimals (or domestic animals, or livestock). For example, swine (or hog)production generates large amounts of excrement. Excrement must bedisposed of in a safe and environmentally friendly manner.

One such disposal process may be the anaerobic digestion of theexcrement in which biogas, containing methane, is produced. Methane is acommodity fuel with economic value. The proceeds from the sale of themethane can be used to reduce the cost of the disposal.

Accordingly, there is a need for the economic production of methane byanaerobic digestion from excrement.

SUMMARY OF THE INVENTION

A method for producing biogas includes: anaerobically digestingexcrement with an additive, the additive including a pre-pupal stage ofan insect from the scientific classification superfamily ofStratiomyoidea; and collecting the biogas. A method for producing anadditive for anaerobic digestion of excrement includes: hatching eggs ofan insect from the scientific classification superfamily ofStratiomyoidea in excrement; growing insect larvae by feeding withadditional excrement; harvesting pre-pupal insect larvae; and grindingthe pre-pupal larvae. An apparatus for producing an additive foranaerobic digestion of excrement includes: a tray having pivot along onelateral side and an upwardly sloping wall terminating with a lip along alateral side opposite the pivot; a flume adjacent the lip; and aconveyor adjacent the pivot.

DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a schematic illustration of an embodiment of a digestion tank.

FIGS. 2A, 2B, and 2C are schematic illustrations of embodiments of anapparatus for producing additive for the production of biogas fromexcrement.

FIG. 3 is a graph illustrating the pH variation per days duringco-digestion of swine manure (SM) and additive (A) at various loadingrates and mixing ratios.

FIG. 4 is a graph illustrating biogas production per day based onvolumetric loading rate during co-digestion of swine manure (SM) andadditive (A) at various loading rates and mixing ratios.

FIG. 5 is a graph illustrating biogas production per day based ondiluted feedstock loading rate during co-digestion of swine manure (M)and additive (A) at various loading rates and mixing ratios.

DESCRIPTION OF THE INVENTION

In general, one invention is directed to a method for producing biogasby the steps of: anaerobically digesting (or anaerobic co-digestion)excrement with an additive; and collecting the biogas. The additive mayinclude a pre-pupal stage of an insect from the scientificclassification superfamily of Stratiomyoidea.

Biogas, as used herein, refers to a gaseous fuel produced by anaerobicdigestion of organic matter and generally contains methane and carbondioxide, among other by-products of the fermentation process. See:Wikipedia, Biogas, incorporated herein by reference.

Anaerobic digestion, as used herein, refers to processes wherebiodegradable materials are broken down, in the absence of oxygen, toproduce, among other things, biogas. See: Wikipedia, Anaerobicdigestion, incorporated herein by reference.

Excrement, as used herein, refers any excrement from any source, forexample, animal or livestock (e.g., pig, cow, goat, sheep, chicken,turkey), and human. See: Wikipedia, Feces, and Wikipedia, Livestock,both incorporated herein by reference.

The additive is used to facilitate biogas production. The additiveincludes a pre-pupal (larva) stage of an insect from the scientificclassification superfamily of Stratiomyoidea. The insect may be of thefamily of Stratiomyidae. The insect may be of the subfamily Hermetiinae.The insect may be of the genus Hermetia. In one embodiment, the insectmay be Hermetia illucens (Black Soldier Fly or BSF larvae or BSFL). SeeWikipedia, Hermetia illucens, and Wikipedia, Holometabolism, bothincorporated herein by reference. The additive may be ground or pureed.The additive may further include frass. The frass may be sourced fromthe insect's excrement generated during the insect's larvae growth. Theadditive, when frass is included, may have an insect:frass ratio (byweight) of 1:0-3.0. In another embodiment, this ratio may be 1:0.5-2.0.In yet, another embodiment, this ratio may be 1:1.0-2.0. And, in anotherembodiment, this ratio may be 1:1.6. Production of the additive isdiscussed below.

Collection of the biogas from the digestion process may be performed inany conventional manner. The collected biogas may be purified tomethane, to enhance value, in any conventional manner.

Generally, digestion may be conducted in a closed tank 10 with agitation12, see FIG. 1. Tank 10 may include, for example: various inlets forcharging excrement 14, additive 16, and water 18; various outlets fordischarge of biogas 20 and sludge 22, sampling ports 24, and accessports 26. The charge (or biomass) is maintained, during digestion, atany temperature that facilitates digestion, for example 39±2° C. Thetank may be charged and maintained during digestion, with excrementdiluted to, in one embodiment, less than 15% water, in anotherembodiment in a range of 5-15% water, in another embodiment in a rangeof 12-14% water, in another 13.7% water, and all subsets thereof. Duringdigestion, the biomass is reloaded, see FIGS. 4 (volume) and 5 (weight),at a rate of 1-7% by volume of the initial mass. In one embodiment, thereload may be in the range of 2-6%, and in another embodiment, in therange of 4-6%, and another, 6%. The reloaded material includes excrement(E) and additive (A) in ratios from 1-2:1-2 (E:A).

Generally, in one embodiment, biogas production, see FIGS. 4 and 5, maybe greater than 1 L/Ld per working volume of the digester. In anotherembodiment, biogas production may be greater than 2 L/Ld. In yet anotherembodiment, biogas production may be greater than 3 L/Ld. In stillanother embodiment, biogas production may be in a range of 1-6 L/Ld.

The additive may be produced by the method of: hatching eggs of theinsect (discussed above) from the scientific classification superfamilyof Stratiomyoidea in excrement; growing larvae of the insect by feedingwith additional excrement; harvesting pre-pupal larvae of the insect;and particle size reduction, (e.g., grinding) the pre-pupal larvae.Additionally, grinding may include pureeing the pre-pupal larvae. Thepre-pupal larvae may also include frass. Any frass not used in theadditive may be collected and used as, for example, fertilizer.

The additive may be producing in an apparatus 100, see FIGS. 2A, 28, and2C, including: a tray 102; a flume 120; and a conveyor 130.

Tray 102 may have a pivot 104 along one lateral side 106 and an upwardlysloping wall 108 terminating with a lip 110 along a lateral side 112opposite the pivot 104. Tray 102 may be compartmentalized. The otherwalls of the tray 102 may be generally vertical (it is believed thatescaping larvae will not or cannot scale the vertical walls andtherefore exit via the sloped wall). The tray 102 may be movable betweena horizontal position (shown in solid lines) and a generally verticalposition (shown in phantom).

The flume 120 may be used to capture pre-pupal larvae exiting the tray102 via the sloped wall 108. Flume 120 may be positioned adjacent to andbelow lip 110. Flume 120 may have a stream of water running therethroughto flush the captured larvae away for particle size reduction (e.g.,grinding, pureeing, and/or homogenizing).

Conveyor 130 is used for removal of frass from the trays 102. Conveyor130 is positioned adjacent to and below the pivoted side 106 of tray102.

Additionally, apparatus 100 may include an excrement feeding system 140for distribution of excrement during the growth of the larvae and growlamps 150.

In use, the tray is filled with excrement, eggs from the insect areplaced in the excrement, larvae hatched from the eggs grow in theexcrement, excrement is added during growth (larvae may consume up toseven times their weight per day in excrement during larvae growth), thepre-pupal stage larvae exit the tray via the sloped wall and arecaptured in the flume, and frass from the growing larvae is dumped ontothe conveyor.

The invention may be further illustrated with reference to the followingexamples.

EXAMPLES

In the following bench-scale examples, various mixtures of swine manure(SM) and additive (A; BSFL) are co-digested diluted to about 13.7%, withsemi-continuous loading (loading every two days), in glass jar digesters(1.893 L with a 1.375 L working volume) with a 21 day hydraulicretention time (HRT) at a temperature of 392° C. and with mixing(swirling digester twice a day) to characterize biogas production atvarious loading rates (additions of volatile solids (VS or SM) andmixing ratios (SM:A). The moisture content of the swine manure averaged83.6% and the moisture content of the additive averaged 75.7%. FIG. 3illustrates the pH variation per days during co-digestion of swinemanure (SM) and additive (A) at various loading rates and mixing ratios.FIG. 4 illustrates biogas production per day based on volumetric loadingrate during co-digestion of swine manure (SM) and additive (A) atvarious loading rates and mixing ratios. FIG. 5 illustrates biogasproduction per day based on diluted feedstock loading rate duringco-digestion of swine manure (M), additive (A), and water (W) at variousloading rates and mixing ratios. In FIGS. 4 and 5, methane concentrationwas in the range of 73-79%.

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicating the scope of the invention.

I claim:
 1. An additive for anaerobic production of biogas fromexcrement comprising: a pre-pupal stage of an insect from the scientificclassification superfamily of Stratiomyoidea, wherein the pre-pupalstage of the insect is subject to a mechanical particle size reductionprocess prior to anaerobic production of the biogas from excrement. 2.The additive of claim 1 wherein the mechanical particle size reductionprocess includes grinding, pureeing, and/or homogenizing.
 3. Theadditive of claim 1 wherein the insect is from the scientificclassification family of Stratiomyidae.
 4. The additive of claim 3wherein the scientific classification subfamily is Hermetiinae.
 5. Theadditive of claim 4 wherein the scientific classification species isHermetia illucens.
 6. The additive of claim 1 wherein the excrement isswine excrement.
 7. The additive of claim 1 wherein the additive furthercomprises frass.
 8. The additive of claim 1 wherein the biogas ismethane.
 9. An additive for anaerobic production of biogas fromexcrement comprising: a pre-pupal stage of an insect from the scientificclassification species is Hermetia illucens, wherein the pre-pupal stageof the insect is subject to a mechanical particle size reduction processprior to anaerobic production of the biogas from excrement, themechanical particle size reduction process includes grinding, pureeing,and/or homogenizing, the excrement includes swine excrement.
 10. Theadditive of claim 9 wherein the additive further comprises frass. 11.The additive of claim 9 wherein the biogas is methane.